Drug-drug co-amorphous systems: An emerging formulation strategy for poorly water-soluble drugs

Overcoming the poor water solubility of small-molecule drugs is a major challenge in the development of clinical pharmaceuticals. Amorphization of crystalline drugs is a highly effective strategy to improve their aqueous solubility. However, amorphous drugs are thermodynamically unstable and likely to crystallize during manufacturing and storage. Recently, drug-drug co-amorphous systems have emerged as a novel strategy to not only enable enhanced dissolution and physical stability of the individual drugs within the system but also to provide a strategy for combination therapy of the same or different clinical indications. This review serves to highlight advances in the methods used to manufacture and characterize drug-drug co-amorphous systems, summarize drug-drug co-amorphous applications reported in recent decades, and provide an outlook on future possibilities and perspectives.

In silico and in vitro investigation of bile salts as coformers for edaravone coamorphous dispersion- Part I

In the present study, we aimed to design the spray-dried coamorphous dispersion (COAM) of a neuroprotective agent-edaravone (EDR) with bile salts to improve oral bioavailability. After the initial screening of different bile salts, EDR-sodium taurocholate (NaTC) COAM showed 4-fold solubility than a pure drug in 1-7pH range. In silico studies to select coformer for COAM revealed a narrow energy gap, easy charge transfer and high chemical reactivity between EDR and NaTC. The optimized EDR-NaTC COAM in a 1:1 molar ratio was characterized for solid state characterizations and in vitro release study. Hydrogen bond formation between the pyrazolone ring of EDR and the -OH group of the phenanthrene ring of NaTC was observed in the ATR-FTIR spectra of COAM. The DSC and XRPD data indicated the formation of an amorphous halo, whereas SEM photographs demonstrated porous, spherical particles of COAM. The pH-independent in vitro drug release of COAM was observed in 0.1N HCl, pH 4.5 and 6.8 buffers which was 3-fold higher than EDR. The COAM was stable for 6 months at accelerated condition without showing a change in drug content or devitrification (Initial: 98.002±0.942%; Accelerated condition: 97.016±1.110%). Although coamorphous form and hydrogen bonding between EDR-NaTC dispersion were primarily responsible for improved dissolution, NaTC, an exceptional surfactant, has also contributed to it. Moreover, its exclusive structural characteristics could prevent the recrystallization of the drug in supersaturated conditions of the GIT and also minimize the effect of food on oral absorption of EDR which will be studied in animals in the second part of this work.

Tranilast-matrine co-amorphous system: Strong intermolecular interactions, improved solubility, and physiochemical stability

There is a great interest to develop co-amorphous drug delivery systems to enhance the solubility of biopharmaceutics classification system (BCS) class II and IV drugs. However, most reported systems only resulted in severalfold solubility improvement. Tranilast (TRA) is an anti-allergic drug used to treat bronchial asthma and allergic rhinitis. It is a BCS class II drug and its poor aqueous solubility affects its absorption in vivo. To address this issue, a natural alkaloid matrine (MAR) with interesting biological activities was chosen to form a co-amorphous system with TRA, based on the solubility parameter and phase solubility experiment. The TRA-MAR drug-drug co-amorphous system was prepared by the solvent evaporation method, and further characterized by powder X-ray diffraction and modulated temperature differential scanning calorimetry. Fourier transform infrared spectroscopy, FT-Raman, and X-ray photoelectron spectroscopy revealed the formation of salt and the presence of strong intermolecular interactions in the TRA-MAR co-amorphous system, which are also supported by molecular dynamics simulations, showing ionic and hydrogen bonding interactions. This co-amorphous system exhibited excellent physical stability at both 25 °C and 40 °C under anhydrous silica gel condition. Finally, co-amorphous TRA-MAR showed greatly enhanced solubility (greater than 100-fold) and rapid release behavior in the vitro release experiments. NMR spectroscopy revealed the strong intermolecular interactions between TRA and MAR in both DMSO‑d₆ and D₂O. Our study resulted in a TRA-MAR co-amorphous drug system with significant solubility improvement and showcased the great potential to improve the dissolution behaviors of BCS class II and IV drugs through the co-amorphization approach.

Improving physicochemical properties and pharmacological activities of ternary co-amorphous systems

The formation of co-amorphous by combining low molecular weight compounds with drugs is a relatively new technology in the pharmaceutical field, which can significantly improve the solubility, dissolution, and stability of poorly water-soluble drugs. However, in our previous studies, the binary co-amorphous system of andrographolide-oxymatrine (AP-OMT) was found to have obvious recrystallization and poor dissolution behavior. Therefore, in this study, we designed three stable ternary co-amorphous systems to improve the physicochemical properties of the binary co-amorphous system of AP-OMT. The ternary co-amorphous systems were prepared with AP, OMT, and trans-cinnamic acid (CA), p-hydroxycinnamic acid (pHCA), or ferulic acid (FA). Intermolecular hydrogen bonds were confirmed by spectroscopy and molecular dynamics simulation. Solubility studies showed that the solubility of the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA was significantly increased compared with that of crystalline AP. Dissolution experiments suggested that the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA exhibited better dissolution behavior without significant recrystallization compared to the binary co-amorphous AP-OMT. The stability study confirmed that the ternary co-amorphous system of AP-OMT-CA/pHCA/FA maintained good physical stability in the long term for 18 months. In addition, pharmacological experiments revealed that the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA have an excellent safety profile and its anti-Alzheimer's disease effects are significantly improved compared to that of the binary co-amorphous systems of AP-OMT. Moreover, this study also found that reducing the pKa value of low molecular weight co-formers would affect the intermolecular interactions and improve the solubility of drugs in the ternary co-amorphous systems. In conclusion, we have successfully prepared ternary co-amorphous systems of AP-OMT-CA/pHCA/FA by amorphization technique, which improves the physicochemical properties of the binary co-amorphous systems of AP-OMT and anti-Alzheimer's disease activity in the Caenorhabditis elegans model. The mechanism for the influence of the pKa value of the co-formers on the physicochemical properties of the ternary co-amorphous system was preliminarily explored, providing theoretical guidance for the development of the ternary co-amorphous system.

Selection of bionic Co-former improves the dissolution of Neohesperidin via Co-amorphous solid dispersion with Naringin

The co-amorphous solid dispersion (c-ASD) is a useful method to enhance water solubility of poorly soluble drugs. The objective of this study was to improve the dissolution of Neohesperidin (NE) via binary c-ASD which, to the best of our knowledge, has not yet been reported. Since NE and Naringin (NA) co-exist abundantly in Chinese herbal medicine Fructus Aurantii Immaturus, it was hypothesised that NA served as a co-former of NE-NA c-ASD to improve the dissolution profile of NE. Hence, NA was selected to prepare c-ASD with NE at a weight ratio of 4:10, 10:10, 10:4 by lyophilisation. They were characterised according to thermal properties, molecular interactions, dissolution properties and physical stability. We found that the 10:10 ratio was the most potent in enhancing the dissolution behaviour of NE; whereby NE and NA are highly synchronous in pair-wise solvation process. A molecular mixture was achieved through the intermolecular H-bond and pi-pi stacking force formed between NE and NA and was stable for 7 -months. We concluded that the NE-NA co-amorphous binary system is a promising strategy to improve the dissolution behaviour and stabilise the amorphous state of NE. Bionic co-former selection may be an innovative and effective way to accurately determine the appropriate co-former of poorly water soluble substances.

Co-amorphous Drug Delivery Systems: a Review of Physical Stability, In Vitro and In Vivo Performance

Over the past few decades, co-amorphous solids have been used as a promising approach for delivering poorly water-soluble drugs. Co-amorphous solids, comprising pharmacologically relevant drug substances or excipients, improve physical stability, solubility, dissolution, and bioavailability compared with single amorphous ingredients. In this review, we have summarized recent advances in physical stability and in vitro and in vivo performances of co-amorphous solids. We have highlighted the role of molar ratio, molecular interaction, and mobility that affects the physical stability of co-amorphous solids. This review delves deep as to how co-amorphous solids affect the physicochemical properties in vitro and in vivo. We also described the challenges to the formulation of co-amorphous solids. A better understanding of the mechanisms of the physical stability, in vitro and in vivo performance of co-amorphous solids, and proper selection of the co-former is likely to expedite the development of robust co-amorphous-based pharmaceutical formulations and can address the challenges associated with the delivery of poorly soluble drugs.

Effect of sodium lauryl sulfate-mediated gelation on the suppressed dissolution of crystalline lurasidone hydrochloride and a strategy to mitigate the gelation

In dissolution test, the surfactant sodium lauryl sulfate (SLS) is usually added to increase the dissolution of insoluble drugs and achieve the sink condition. However, the current study found that 0.1 % SLS would significantly decrease the dissolution of crystalline lurasidone hydrochloride (LH, a BCS Ⅱ drug). The aim of this study was to clarify the mechanism of this unexpected phenomenon and explore a strategy for mitigating the negative effect of SLS on the dissolution of LH. Sample characterizations (such as PLM, DSC, PXRD, IR and NMR) confirmed that the insoluble single-phase amorphous LH-SLS complex (with a single T_g at 35.2 °C) formed during dissolution in 0.1 % SLS aqueous solution via electrostatic interaction, tetrel bond interaction, and hydrophobic effect. Due to the plasticization effect of water, the transition of amorphous LH-SLS from its glassy state to viscous supercooled liquid state led to the gel formation, and suppressd the dissolution of LH. Meanwhile, the solubility curve of LH in SLS aqueous solution at various concentrations exhibited an unusual V-shaped feature, with the CMC value of SLS serving as the inflection point, since the gel degree was attenuated due to the micelle solubilization of SLS. Additionally, an innovative strategy was developed to alleviate the inhibiting effect of SLS on LH dissolution based on the potential competitive interactions. This study not only enriches the internal mechanism of surfactant-inhibited drug dissolution but also informs an effective strategy to mitigate the gelation.

Theoretical exploration of the binding selectivity of inhibitors to BRD7 and BRD9 with multiple short molecular dynamics simulations

Bromodomain-containing proteins 7 and 9 (BRD7 and BRD9) have been considered as potential targets of clinical drug design toward treatment of human cancers and other diseases. Multiple short molecular dynamics simulations and binding free energy predictions were carried out to decipher the binding selectivity of three inhibitors 4L2, 5U6, and 6KT toward BRD7 and BRD9. The results show that 4L2 has more favorable binding ability to BRD7 over BRD9 compared to 5U6 and 6KT, while 5U6 and 6KT possess more favorable associations with BRD9 than BRD7. Furthermore, estimations of residue-based free energy decompositions further identify that four common residue pairs, including (F155, F44), (V160, V49), (Y168, Y57) and (Y217, Y106) in (BRD7, BRD9) generate obvious binding differences with 4L2, 5U6, and 6KT, which mostly drives the binding selectivity of 4L2, 5U6, and 6KT to BRD7 and BRD9. Dynamic information arising from trajectory analysis also suggests that inhibitor bindings affect structural flexibility and motion modes, which is responsible for the partial selectivity of 4L2, 5U6, and 6KT toward BRD7 and BRD9. As per our expectation, this study theoretically provides useful hints for design of dual inhibitors with high selectivity on BRD7 and BRD9.

Bromodomains (BRDs) are structurally conserved epigenetic reader modules observed in numerous chromatin- and transcription-associated proteins that have a capability to identify acetylated lysine residues.

Coamorphous System of Florfenicol-Oxymatrine for Improving the Solubility and Dissolution Rate of Florfenicol: Preparation, Characterization and Molecular Dynamics Simulation

Coamorphous system has proved to be an effective approach to improve the solubility of BCSⅡ drugs. Florfenicol (FF) is a widely used veterinary antibiotic but has poor aqueous solubility. Therefore, the coamorphous system of florfenicol and oxymatrine (OMT) formulated at 1:1 and 1:2 M ratios were prepared by using solvent evaporation, followed by a series of characterization in terms of PXRD, DSC, FTIR and Raman spectroscopy. It was found that FF and OMT are miscible according to Hansen solubility parameters. The molecular electrostatic potential (MEP) and radial distribution function (RDF) analysis demonstrated the possible hydrogen bond interaction in coamorphous system, which was confirmed by FTIR and Raman spectra. The coamorphous FF-OMT (1:1) maintained stability for 60 days at 25 °C/0% RH and 30 days at 40 °C/75% RH, which may be attributed to better molecular miscibility of FF and OMT and the strong hydrogen bond of O-H (FF)⋯O-N (OMT) and N-H (FF)⋯O-N (OMT). In addition, the apparent solubility and permeability, dissolution and intrinsic dissolution rate (IDR) of the acquired coamorphous solids were obviously increased compared with crystalline FF. In conclusion, a drug-drug coamorphous formulation can be applied to improve the solubility and dissolution of crystalline FF.

Influence of the pK a Value of Cinnamic Acid and P-Hydroxycinnamic Acid on the Solubility of a Lurasidone Hydrochloride-Based Coamorphous System

Coamorphization of a poorly water-soluble active pharmaceutical ingredient (API) has been proven to be effective in improving its solubility. Generally, API can form multiple coamorphous systems with different coformers. However, it remains unclear how the pK _a value of different coformers influences the solubility of the API. In this study, structurally related cinnamic acid (CA, pK _a = 4.37) and p-hydroxycinnamic acid (pHCA, pK _a = 4.65) were chosen as coformers for the coamorphization of lurasidone hydrochloride (LH). To investigate the influence of the pK _a value of the coformers on the solubility of LH, LH-CA/pHCA coamorphous systems were prepared by the vacuum rotary evaporation method and characterized by powder X-ray diffraction and differential scanning calorimetry. Fourier-transform infrared spectroscopy, Raman spectroscopy, and molecular dynamics (MD) simulations were employed to investigate the intermolecular interaction of the coamorphous systems. It was found that the solubility of LH in the coamorphous LH-pHAC with a higher-pK _a coformer was higher than that of the coamorphous LH-CA. In addition, according to the solubility product principle-based formula derivation, we established the functional relationship between the solubility of LH and the pK _a of the coformers at different-pH buffering solution. It was found that the coformer with a larger pK _a value would be more beneficial to improve the solubility profile of LH. Collectively, the current study offers an effective strategy to improve the poor solubility of drugs by increasing the pK _a value of the coformer in coamorphous systems.